1. Field of the Invention
The present invention relates to a stamped yoke member of a Cardan joint, being more specifically used in steering columns of automotive vehicles, and more particularly in steering columns provided with an assistance device.
2. Description of the Related Art
The current steering column of an automotive vehicle comprises two portions: a top portion, which is connected to the steering wheel, and a middle portion which is connected to the gearbox that controls a steering rod for the steering wheels. The top portion and the middle portion are connected with each other by a homokinetic joint, called a Cardan joint.
The middle portion is also connected to the pinion of the gearbox through a homokinetic joint or a Cardan joint. Each of the two Cardan joints comprises a cross-piece arranged between two yoke members. As far as the Cardan joint of the top portion is concerned, one of the yoke members is connected to the top portion and the other one is connected to the middle portion.
As far as the Cardan joint of the steering pinion is concerned, one of the yoke members is connected to the middle portion, and the other one is connected to the steering pinion.
When the steering column comprises an assistance device, the latter can consist in an electric system or a hydraulic system.
For both systems, there are two types of assisted steering gear depending on the assistance device arrangement: either the assistance device is arranged on the top portion of the steering column, this is the column assisted steering gear, or the assistance device is arranged directly on the steering rack, this is the pinion assisted steering gear, referring to the steering pinion driving the rack.
In the case of an electric or hydraulic assisted steering gear, a high torque is to be transmitted at the assistance outlet, i.e. at the motion outlet in the top portion of the column.
The high torque is therefore to be transmitted upstream the middle portion of the column, i.e. upstream each of both transmission Cardan joints which are arranged at each end of the column middle portion, on the one hand, on the top portion side of the column and, on the other hand, on the steering pinion side. Since each transmission Cardan joint comprises two yoke members of Cardan joint, there are thus four yoke members of Cardan joint that should be able to transmit a high torque.
In the case of a pinion electric assisted steering gear and in the case of the pinion hydraulic assisted steering gear, the high torque is directly applied on the rack. The torque transmitted by the top portion of the column and by the middle portion of the column is thus relatively low. This is also true for all four yoke members of Cardan joint, which transmit a relatively low torque.
There are stamped yoke members of Cardan joint such as shown and designated by reference numeral 10 on FIG. 5, which is obtained through deforming a thick metal sheet without modifying the thickness. For this purpose, a blank is cut from the metal sheet, the thickness of which depends on its extending abilities so as to give it the final shape through stamping. The yoke member 10 of Cardan joint is mounted and immobilized on a non shown transmission shaft 5, the transmission axis of which is denoted 6. A tightening system is provided by a screw with a tightening axis 4, said tightening screw being mounted on two pliers 111 and 112 in order to bring them nearer one to the other so as to immobilize the yoke member 10 on the transmission shaft 5. In order to provide the pliers 111 and 112, the metal sheet is folded on itself. In the case where there is a high tightening torque and a high rotation torque on the transmission shaft, some sliding occurs between both portions one relative to the other on each of both pliers 111 and 112. Such a sliding results in the loosening of the tightening screw and in some play between the transmission shaft 5 and the yoke member 10. In the case of an excessively strong tightening, there is some contact between the pliers returns, resulting in a lack of tightening on the transmission shaft.